1. Field of the Invention
This invention relates to apparatus for lighting an appliance dial and, more particularly, to backlighting for a control dial of a refrigerator using light generated by a remote compartment lamp.
2. Background of the Invention
Various household appliances, e.g. refrigerators, are provided with indexed dials that are manually operated by a user to obtain a selected performance setting. Such dials are frequently connected to high voltage control elements of the appliance and are rotatably supported in the cabinet of the appliance, so that only a small portion of the dial is accessible by the user. Since the user often has wet hands while using the appliance, as an important safety feature the dial supporting structure is typically designed to shield the user from sources of electricity.
From both practical and cosmetic considerations, it is highly desirable to provide backlighting for the indexed information on such control dials, so that a user may know precisely which setting is chosen even when the ambient lighting is inadequate to fully illuminate the indexed surface of the dial. For both safety and convenience, therefore, it is particularly desirable to backlight only a selected portion of the indexed surface of the dial without locating electrically powered lightbulbs immediately adjacent thereto.
It is known to illuminate an object by means of a transparent, generally cylindrical, transparent element commonly known as a "lightpipe" to propagate light generated from a remote source to the vicinity of a surface of the object. The most convenient light source for use with such a light pipe in an appliance is generally the compartment lamp for the appliance, e.g., the refrigerator compartment.
However, the commonly used form of the cylindrical control dial, rotatably mounted on a shaft, presents two major obstacles to positioning the discharge end of a light pipe directly behind the forward face of the dial in order to backlight the indicia thereon. First, the central location of the mounting shaft within the cylindrical dial body prevents direct lighting access to the outwardly most visible portion of the dial face from the rear thereof. Second, the dial has a perimeter wall that prevents a lightpipe from approaching the rear of the face directly.
Although it is possible to form a transparent lightpipe into a serpentine shape in order to place the light-delivering end directly behind the dial surface most visible to a user, such a structure would involve very tight radii that would cause significant loss of illumination by the light being conducted in the lightpipe. Also, to prevent any accidental electrically-conductive contact between a user and the high voltage elements of the appliance, the lightpipe is best passed through a confining opening in the appliance structure to be cantilevered behind the visible surface of the dial. Finally, keeping in mind that appliances will be subject to considerable shock and vibration during transportation to the user and, once in service, have doors that are frequently slammed and motors that cause vibration, it is imperative that the light-delivering end of the lightpipe be precisely and firmly supported within the structure.
Various solutions, none of which utilize cantilevered lightpipes, have been attempted by persons skilled in the art, with varying success. Thus, for example, U.S. Pat. No. 3,040,458, to Mathews, discloses the use of a lighted bulb very close to a transparent ring surrounding an indexed cylindrical surface of a control dial. The light rays entering the transparent ring at an angle from the light source are retained by internal reflection within the transparent ring and are reflected outward from the numerals or indicia of the control dial at a display window. It is pointed out in this patent that there can be no wetting of the interface between the transparent ring 2 and the outer surface of the dial, e.g., as may be the case where there is condensation in a kitchen, as this would frustrate the effectiveness of the system.
U.S. Pat. No. 2,737,744, to Sturges et al, utilizes a plurality of light bulbs located within holes in a transparent element which is shaped to funnel light to both sides of a plurality of dials that are lighted from the sides.
U.S. Pat. No. 3,278,738 to Clark, teaches the use of carefully bonded optical fibers with shaped ends to transmit light from one end of the optical fiber bundle to direct emitted light to a selected small portion of a dial.
U.S. Pat. No. 4,383,288, to Hess, II et al, discloses a light collector structure that includes a lens portion with angled sections for gathering light from a broad area and provided with a circular groove that snugly fits into a portion of the supporting structure.
U.S. Pat. No. 2,290,278, to Failla, discloses the use of a clamped lightpipe that conveys light from a remote light bulb to the adjacently placed central hubs of a minute and an hour hand of a clock, so that the light is conveyed through these hands and out their distal ends to be directed to numbers provided on the clock dial.
None of these prior art devices solves the specific problem addressed by this invention, namely the provision of precisely directed lighting to safely backlight the surface of a rotatable dial which is connected to high voltage elements of a refrigerator or other household appliance.
A need, therefore, exists for a sturdy lightpipe system that efficiency and safely transmits light from a remote source to precisely backlight selected indicia on a rotatable and user-touchable control dial for a household appliance.